This invention relates to a radiation scanning and detecting system.
One prior art system of this kind, for instance as described and claimed in U.S. Pat. No. 3,448,267, filed on Oct. 27, 1965, by Richard Blythe et al, N. Harbour, Mich., assignors to the Bendix Corporation, a corporation of Delaware, and entitled "Apparatus for infra-red scanning having a variable detector aperture and a variable bandwidth amplifier", comprises a radiation detector which is responsive to radiation from a projected ground image of the detector as focused by an optical system. The projected ground image is scanned across the terrain by means of an optical scanner, while an amplified detector output is recorded. To improve the performance of this system in providing a radiation strip map from the recorded and processed data, either the effective sensing area of the detector comprising a single detector element, or the electrical bandwidth of the system, or both are varied automatically as a function of an average ambient radiation level. To this end a variable spatial filter is disposed along the optical path between the optical system and the detector. This spatial filter comprises a fixed optical stop member and a movable stop member that in response to a control signal applied thereto controls the size of an aperture and therefore functions as a diaphragm which controls the effective size of the detector sensing area. This arrangement is bound to a certain physical distance between the detector and the diaphragm. Consequently, this diaphragm will not be solely effective as a "field" diaphragm, but will also cause half-shadow effects to occur; in other words, due to the physical distance a certain amount of available radiation from the ground will be blocked from reaching the detector, so that less useful radiation will be incident upon the detector area. Therefore an increase of resolution achieved by a decrease of the aperture size of the diaphragm is bought at the cost of a decrease in useful radiation incident upon the detector sensing area. Consequently, the signal-to-noise ratio will be decreased when the resolution is increased. According to this known system, an increase of the resolution, caused when the incoming radiation level is relatively high, is accompanied by a corresponding increase of the system bandwidth to be compatible with the size of the resolution cell projected on the ground and to pass high frequency components incident to the higher resolution; due to this increased bandwidth the signal-to-noise ratio is further degraded. Furthermore, due to the electro-mechanical nature of the spatial filter the response to radiation level variations is limited.
U.S. Pat. No. 3,723,642, entitled "A thermal display system", relates to a radiation scanning and detecting system wherein the scanned signals are processed in a certain manner. Such a system comprises a linear array of equally sized detector elements. An optical scanner is provided for scanning a field of an image in accordance with a two-dimensional frame; an optical system produces a stationary beam from the scanner output, which beam is directed to the focal plane of the detector array. The individual video signals produced by each of the detector elements of the array during each line scan, are each representative of the same line being scanned. By appropriately processing, more in particular delaying the individual video signals derived from the detector elements, and then adding the signals thus delayed, the system performance, more in particular the signal-to-noise ratio, can be improved in a relatively simple and reliable manner.
However, the characteristics of the ultimately reproduced and/or recorded output signal representing the scanned field of image, cannot be varied and/or adapted to variable parameters in which the vehicle carrying the radiation scanning and detecting system is to operate, because such characteristics basically are determined by the fixed configuration of the detector elements. Only by varying the number and/or physical configuration of the detector elements such characteristics can be varied.